A Loran-C carrier phase tracking method and system considering sky wave interference influence

Abstract

The application discloses a Loran-C carrier phase tracking method and system considering sky wave interference, and relates to the technical field of radio signal reception. The specific implementation scheme is as follows: a sky wave and a ground wave are separated to obtain an amplitude ratio and a time delay difference, and whether the sky wave is strong is determined according to the amplitude ratio; a phase discrimination correction number is calculated based on the amplitude ratio and the time delay difference, and an integral interval A of in-phase branch and quadrature branch signals of a carrier phase tracking loop is determined; the in-phase branch signal and the quadrature branch signal are integrated according to the integral interval A, a phase discrimination result is calculated, the phase discrimination result is corrected to obtain a phase discrimination correction value; and the local carrier is adjusted based on the phase discrimination correction value to realize carrier phase tracking. The method of the application expands the effective length of the Loran-C signal used for carrier phase tracking, optimizes the phase discrimination process of the Loran-C carrier phase tracking algorithm, and improves the carrier phase tracking performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radio signal receiving, in particular to a Loran-C carrier phase tracking method and system considering the influence of sky wave interference. BACKGROUND

[0002] The Loran-C and the new generation of eLoran receiver adopt carrier phase tracking technology to lock the received signal, in order to avoid the influence of sky wave, the current carrier phase tracking technology mainly selects the ground wave signal to realize. The prior art has less research on the influence of sky wave interference on carrier phase tracking, and in engineering practice, the ground wave third cycle signal is often used for carrier phase tracking without the influence of sky wave.

[0003] Generally, with the increase of the propagation distance of Loran-C ground wave signal, the received signal-to-noise ratio of the signal is lower and lower, the amplitude ratio of the sky wave to the ground wave is larger and larger, and the time delay of the sky wave to the ground wave is smaller and smaller. The relatively strong sky wave interference usually occurs in a place far from the transmitting station of the Loran-C receiver, at this time, the signal-to-noise ratio is low, the relative time delay of the sky wave to the ground wave is small, the noise and distortion of the whole signal is large, and the length of the pure ground wave signal is short and the estimation deviation of the starting time of the ground wave signal is large. In the strong sky wave interference scene, if only the ground wave signal is selected for carrier phase tracking, it will have an adverse effect on the carrier phase tracking accuracy.

[0004] The prior art can adapt to the case that the Loran-C signal quality is high, if the received signal quality decreases, the carrier phase tracking accuracy will be affected. In order to improve the carrier phase tracking accuracy, the effective length of the Loran-C signal used for carrier phase tracking should be as large as possible.

[0005] SUMMARY

[0006] Based on this, in order to solve the problem of poor carrier phase tracking performance caused by sky wave interference, the present application provides a Loran-C carrier phase tracking method and system considering the influence of sky wave interference.

[0007] The present application provides a Loran-C carrier phase tracking method considering the influence of sky wave interference, comprising:

[0008] The amplitude ratio and time delay difference of the sky wave and the ground wave are obtained by using the sky-ground wave separation technology, and whether it is strong sky wave is judged according to the amplitude ratio of the sky wave and the ground wave;

[0009] The phase discrimination correction number is calculated based on the amplitude ratio and time delay difference of the sky wave and the ground wave, and the integration interval A of the in-phase branch and the quadrature branch signal of the carrier phase tracking loop is determined;

[0010] According to the integral interval A, the in-phase branch signal and the quadrature branch signal are integrated, and a phase discrimination result is calculated, and a phase discrimination correction value is obtained by correcting the phase discrimination result;

[0011] The local carrier is adjusted based on the phase discrimination correction value, so as to realize carrier phase tracking.

[0012] The amplitude ratio and time delay difference of the sky wave and the ground wave are obtained by,

[0013] The sky wave and the ground wave are separated by using a sky wave and ground wave separation technology in a sky wave and ground wave separation module, so as to realize Loran-C signal sky wave and ground wave identification, and obtain the amplitude ratio SGR and the time delay difference Δt of the sky wave and the ground wave.

[0014] The sky wave and ground wave separation technology uses a frequency spectrum division method.

[0015] The strong sky wave is determined by,

[0016] A threshold value is set, when the amplitude ratio SGR of the sky wave and the ground wave is greater than the threshold value, it is a strong sky wave, and when the amplitude ratio SGR of the sky wave and the ground wave is not greater than the threshold value, it is a non-strong sky wave.

[0017] The calculation of the phase discrimination correction number E(SGR, Δt) includes,

[0018]

[0019] Wherein, ω c represents the carrier angular frequency of the Loran-C signal, k0 represents the threshold of the strong sky wave, Δt represents the time delay difference, and arctan(·) represents the four-quadrant inverse tangent operator;

[0020] SGR is taken as a critical point when k0, if SGR≤k0, it is a non-strong sky wave interference, and if SGR>k0, it is a strong sky wave interference.

[0021] The determination of the integral interval A includes,

[0022] The in-phase branch and the quadrature branch use the same integral interval, and the integral interval A is determined according to the amplitude ratio SGR of the sky wave and the ground wave and the threshold k0 of the strong sky wave;

[0023] The calculation of the integral interval A includes,

[0024]

[0025] Wherein, t a , t b respectively define the upper limit and the lower limit of the integral interval of the ground wave signal in a Loran-C pulse signal, l P represents the pulse signal time length, and t grirepresents the current Loran-C pulse signal starting time.

[0026] The phase discriminator result acquisition includes,

[0027] The carrier phase tracking loop adopts a Costas loop structure, the Loran-C signal is multiplied by a sine carrier and a cosine carrier respectively, and is filtered by a low-pass filter (LPF) to obtain an in-phase branch signal i(t) and a quadrature branch signal q(t). The i(t) and q(t) are integrated according to the integration interval A, and the integration results of the in-phase and quadrature branch signals of the reference pulse signal in each GRI period are I(t gri ) and Q(t gri ). The integration results of the in-phase and quadrature branch signals I(t gri ) and Q(t gri ) are sent to a phase discriminator, and a phase discriminator result E(t gri ) is output.

[0028] The phase discriminator result E(t gri ) calculation includes,

[0029]

[0030] Wherein, arctan(·) represents a four-quadrant inverse tangent operator, I(t gri ) represents the integration result of the in-phase branch, and Q(t gri ) represents the integration result of the quadrature branch.

[0031] The phase discriminator correction value calculation includes,

[0032] Based on the phase discriminator result E(t gri ) and the phase discriminator correction E(SGR,△t), the phase discriminator correction value is calculated.

[0033] E ％ (t gri ) = E(t gri ) + E(SGR,△t)

[0034] Wherein, E ％ (t gri ) represents the phase discriminator correction value.

[0035] The local carrier adjustment includes,

[0036] The phase discriminator correction value E ％ (t gri ) is sent to the loop filter of the Costas carrier phase tracking loop, the frequency control word is calculated, the VCO output frequency is adjusted, and the adjustment of the local carrier signal is realized.

[0037] The application also provides a Loran-C carrier phase tracking system considering sky wave interference, comprising:

[0038] a data acquisition unit configured to acquire the amplitude ratio and time delay difference of the sky wave and ground wave by using a sky wave and ground wave separation technology;

[0039] a judgment module configured to judge whether the sky wave is strong according to the amplitude ratio of the sky wave and ground wave;

[0040] a calculation module configured to calculate a phase discrimination correction number based on the amplitude ratio and time delay difference of the sky wave and ground wave, determine the integral interval A of the in-phase branch signal and quadrature branch signal of the carrier phase tracking loop, integrate the in-phase branch signal and quadrature branch signal according to the integral interval A, calculate a phase discrimination result, and correct the phase discrimination result to obtain a phase discrimination correction value;

[0041] an adjustment module configured to adjust the local carrier based on the phase discrimination correction value to realize carrier phase tracking.

[0042] Beneficial effects:

[0043] 1. The effective length of the Loran-C signal used for carrier phase tracking is extended. The signal interval length used for carrier phase tracking is essentially extended. In a non-strong sky wave interference scenario, the effective signal determined by the upper limit and lower limit of the integral interval of the ground wave signal is used, and in a strong sky wave interference scenario, the entire pulse signal is used. Thus, the signal interval length used for carrier phase tracking is extended to improve the carrier phase tracking performance.

[0044] 2. The phase discrimination process of the Loran-C carrier phase tracking algorithm is optimized. In a sky wave interference scenario, a shorter ground wave signal does not have to be used, the difficulty of realizing carrier phase tracking in a sky wave and ground wave mixed signal is reduced, the phase discrimination correction number caused by the sky wave interference to the carrier phase tracking error is calculated based on the amplitude ratio and time delay difference of the sky wave and ground wave, is used to compensate the phase discrimination result, and finally ensures that the local carrier phase reproduced after the carrier phase tracking using the sky wave and ground wave mixed signal can be reliably synchronized with the carrier phase of the Loran-C received signal ground wave segment.

[0045] 3. In a strong sky wave scenario, the requirement of the carrier phase tracking to the ground wave signal position estimation accuracy is reduced. The technical scheme of the application uses the entire signal segment data to respectively integrate the in-phase branch and quadrature branch in a strong sky wave interference scenario. Therefore, it is only required to ensure that the integral interval contains the entire effective signal segment, without the need to know the accurate ground wave signal position. The operation of the carrier phase tracking module is more independent, the adverse effects of the poor real-time estimation accuracy of the ground wave position in a strong sky wave scenario on the carrier phase tracking module are avoided, and the carrier phase tracking performance is improved.

[0046] It is to be understood that the details set forth herein do not limit the scope of the application. Other aspects of the application will become apparent to those skilled in the art upon reading the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0047] The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification. In the drawings:

[0048] Figure 1 is a principle block diagram of a carrier phase tracking method considering the influence of sky wave interference according to the first embodiment of the application;

[0049] Figure 2 is a signal interval, i.e. Loran-C signal, schematic diagram for carrier phase tracking according to the second embodiment of the application;

[0050] Figure 3 is a digital system implementation function block diagram of a carrier phase tracking method considering the influence of sky wave interference according to the second embodiment of the application. DETAILED DESCRIPTION

[0051] Exemplary embodiments of the application are described herein with reference to the accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments described herein are illustrative of the present application and should not be construed as limiting the scope of the application. Those skilled in the art will readily recognize various modifications and changes that can be made thereto without departing from the scope and spirit of the application as defined by the following claims.

[0052] Embodiment 1

[0053] As Figure 1 , the first embodiment of the application provides a Loran-C carrier phase tracking method considering the influence of sky wave interference, comprising:

[0054] S1: using sky-ground wave separation technology to obtain the amplitude ratio and time delay difference of sky wave and ground wave, and determining whether it is strong sky wave according to the amplitude ratio of sky wave and ground wave. It should be noted that:

[0055] The obtaining of the amplitude ratio and time delay difference of sky wave and ground wave comprises,

[0056] In the sky-ground wave separation module, sky-ground wave separation technology is used to realize Loran-C signal sky-ground wave identification, to obtain the amplitude ratio SGR and time delay difference At of sky wave and ground wave, and to obtain the approximate position of ground wave;

[0057] The sky-ground wave separation technology uses frequency spectrum division method.

[0058] The frequency spectrum division method is preferably adopted in the sky-wave and ground-wave separation technology. In order to improve the estimation accuracy of the amplitude ratio SGR and the time delay difference At of the sky-wave and ground-wave, the sliding average of N times of calculation results can be adopted, and the typical value of N is 20-100.

[0059] The judgment of the strong sky-wave includes,

[0060] A threshold is set. When the amplitude ratio SGR of the sky-wave and ground-wave is greater than the threshold, it is a strong sky-wave. When the amplitude ratio SGR of the sky-wave and ground-wave is not greater than the threshold, it is a non-strong sky-wave.

[0061] S2: Calculate the phase detection correction based on the amplitude ratio and the time delay difference of the sky-wave and ground-wave, and determine the integral interval A of the in-phase branch and the quadrature branch signals of the carrier phase tracking loop. It should be noted that:

[0062] The calculation of the phase detection correction E(SGR, At) includes,

[0063]

[0064] Wherein, ω c represents the carrier angular frequency of the Loran-C signal, k0 is a constant representing the threshold of the strong sky-wave, At represents the time delay difference, arctan(·) represents the four-quadrant inverse tangent operator, and the value range of E(SGR, At) is (-π, π];

[0065] Take SGR as k0 as the critical point. If SGR≤k0, it is a non-strong sky-wave interference. If SGR>k0, it is a strong sky-wave interference.

[0066] S3: Integrate the in-phase branch signal and the quadrature branch signal according to the integral interval A, and calculate the phase detection result. The phase detection result is corrected to obtain the phase detection correction value. It should be noted that:

[0067] The determination of the integral interval A includes,

[0068] The in-phase branch and the quadrature branch adopt the same integral interval. The integral interval A is determined according to the amplitude ratio SGR of the sky-wave and ground-wave and the threshold k0 of the strong sky-wave.

[0069] The calculation of the integral interval A includes,

[0070]

[0071] Wherein, t a , t b are respectively defined in a Loran-C pulse signal to represent the upper limit and the lower limit of the integral interval of the ground-wave signal, l P represents the pulse signal time length, and t gri represents the starting time of the current Loran-C pulse signal.

[0072] Preferably, since the signal strength of the ground wave signal is relatively weak in the first and second periods, the lower limit t of the ground wave signal integration interval described in this application is... a This is the zero-crossing point of the second cycle of the ground wave signal; t b Take the start time of the skywave signal, i.e., t. b =t a +△t+20(μs).

[0073] Preferably, the threshold value k0 for strong skywave is 5dB.

[0074] Preferably, in order to reduce phase detection error, the range of the integration interval A should be as large as possible within the effective signal range.

[0075] The acquisition of phase detection results includes,

[0076] The carrier phase tracking loop adopts a Costas loop structure. The Loran-C signal is multiplied by the sine carrier and cosine carrier respectively, and then filtered by a low-pass filter (LPF) to obtain the in-phase branch signal i(t) and the quadrature branch signal q(t). i(t) and q(t) are integrated according to the integration interval A. The integration results of the in-phase and quadrature branches of the reference pulse signal for each GRI cycle are I(t). gri ), Q(t) gri ), and integrate the results of the in-phase and quadrature branches I(t) gri ), Q(t) gri The signal is fed into the phase detector, and the phase detection result E(t) is output. gri ).

[0077] Phase detection result E(t) gri The calculation includes,

[0078]

[0079] Where arctan(·) represents the four-quadrant arctangent operator, i.e., E(t) gri The range of I(t) is (-π,π], gri ) represents the integral result of the in-phase branch, Q(t) gri ) represents the integral result of the orthogonal branch.

[0080] Preferably, the -3dB target cutoff frequency of the low-pass filter LPF is 10kHz. When this application is applied to a digital system, an FIR low-pass filter can be used, and the filter model can be selected as a 127th order Hanning window.

[0081] The calculation of the phase detection correction value includes,

[0082] Based on the phase detection result E(t) gri ) and the phase detection correction number E(SGR,△t), calculate the phase detection correction value;

[0083] E ％ (t gri )=E(t gri )+E(SGR,△t)

[0084] wherein E ％ (t gri ) represents the phase discrimination correction value, the value range of E ％ (t gri ) is normalized to (-π, π].

[0085] S4: adjusting the local carrier based on the phase discrimination correction value to realize carrier phase tracking. It should be noted that:

[0086] the adjustment of the local carrier includes,

[0087] sending the phase discrimination correction value E ％ (t gri ) into the loop filter of the Costas carrier phase tracking loop to calculate the frequency control word and adjust the VCO output frequency to realize the adjustment of the local carrier signal.

[0088] Preferably, the loop filter is a second-order loop filter, and the theoretical steady-state phase difference is 0 when it is locked, so that the frequency and phase of the local carrier are both locked on the ground wave of the received signal.

[0089] Preferably, the damping coefficient of the selected second-order loop filter is 0.707; the equivalent noise bandwidth is determined and adjusted according to the tracking accuracy and tracking range of the phase-locked loop, and the reference value is 5 Hz.

[0090] The second aspect of the embodiment provides a Loran-C carrier phase tracking system considering the influence of sky wave interference, comprising:

[0091] a data acquisition unit configured to acquire the amplitude ratio and time delay difference of the sky wave and the ground wave by using the sky-ground wave separation technology;

[0092] a judgment module configured to judge whether it is a strong sky wave according to the amplitude ratio of the sky wave and the ground wave;

[0093] a calculation module configured to calculate the phase discrimination correction based on the amplitude ratio and the time delay difference of the sky wave and the ground wave, and determine the integration interval A of the in-phase branch signal and the quadrature branch signal of the carrier phase tracking loop; integrate the in-phase branch signal and the quadrature branch signal according to the integration interval A, and calculate the phase discrimination result; and correct the phase discrimination result to obtain the phase discrimination correction value;

[0094] an adjustment module configured to adjust the local carrier based on the phase discrimination correction value to realize carrier phase tracking.

[0095] The present application optimizes the prior art in the non-strong sky wave interference scene, that is, according to the sky-ground wave separation technology, the time delay of the sky wave relative to the ground wave and the ground wave signal interval are determined, so that the effective length of the ground wave signal interval for carrier phase tracking is maximized; when strong sky wave interference occurs, the entire pulse signal is used for carrier phase tracking. By maximizing the use of Loran-C signals, accurate tracking performance can be obtained by directly tracking the ground wave signal when the sky wave interference is relatively weak and the ground wave signal is relatively strong, and relatively stable and reliable tracking results can be obtained when the sky wave interference is relatively strong and the ground wave signal is relatively weak.

[0096] Embodiment 2

[0097] As Figures 2-3 , the first embodiment of the present application, which is different from the first embodiment, provides a verification test of a Loran-C carrier phase tracking method and system considering the influence of sky wave interference. To verify the technical effects used in the present method, the present embodiment compares the test results of the traditional technical solution and the present method by scientific demonstration means, to verify the real effects of the present method.

[0098] In the present embodiment, a Loran-C signal simulator is used to simulate Loran-C signals in strong sky wave scenarios and non-strong sky wave scenarios respectively, to build a test environment. The recurring carrier of the 100th GRI cycle of the carrier tracking module of the present method and the current traditional method is grabbed respectively, the difference between the standard Loran-C signal theoretical third week zero crossing point and the nearest recurring carrier zero crossing point is compared, and the difference is taken as the carrier tracking error.

[0099] The specific test scheme includes:

[0100] Scheme 1: The signal interval described in the present application is the entire pulse signal containing the ground wave and sky wave signals, and the carrier phase tracking phase correction number is used to compensate the phase comparison result;

[0101] Scheme 2: The signal interval described in the present application is the ground wave signal second week zero crossing point (i.e. the ground wave 20μs position) to all effective signals before the arrival of the sky wave signal, and the carrier phase tracking phase correction number is not used;

[0102] Scheme 3: The signal interval in the traditional practice is the ground wave signal third cycle signal (i.e. the signal interval from 20μs to 30μs of the ground wave), and the carrier phase tracking phase correction number is not used.

[0103] The signal interval used for carrier phase tracking in each test scheme and the Loran-C signal schematic diagram are shown in Figure 2 .

[0104] During the implementation of the test scheme, the reference signal of the Loran-C signal simulator is used to determine the theoretical ground wave signal starting position (i.e. the ground wave 0 μs position) of the simulator output pulse, and then the theoretical third cycle zero-crossing position (i.e. the ground wave 30 μs position) is obtained. The theoretical third cycle zero-crossing position is taken as the reference point, the positive zero-crossing position of the reproduced carrier wave closest to the reference point when the carrier tracking loop is stable is taken as the measured value, and the carrier phase tracking error is counted.

[0105] The specific test scenarios include scenario one and scenario two, wherein scenario one simulates strong sky wave interference, and scenario two simulates non-strong sky wave interference.

[0106] Scenario one: the simulator is set to a signal-to-noise ratio of -8 dB (including Gaussian noise and near-frequency continuous wave interference), the sky wave / ground wave amplitude ratio SGR is 10 dB, and the sky wave relative to the ground wave time delay is 44.375 μs;

[0107] Scenario two: the simulator is set to a signal-to-noise ratio of -3 dB (including Gaussian noise and near-frequency continuous wave interference), the sky wave / ground wave amplitude ratio SGR is 3 dB, and the sky wave relative to the ground wave time delay is 49.375 μs;

[0108] For scenario one and scenario two, the carrier phase tracking loop used in the present example has been in a stable tracking state at the 100th GRI cycle, so the positive zero-crossing position of the reproduced carrier wave closest to the reference point at the 100th GRI cycle is taken as the measured value, and the carrier phase tracking error statistics are shown in Table 1 and Table 2, respectively.

[0109] Table 1: Carrier phase tracking error statistics table for scenario one

[0110] Serial number Scheme 1 measurement (μs) Scheme 2 measurement (μs) Scheme 3 measurement (μs) 1 30.2057 29.9441 30.1311 2 29.9996 30.7495 29.7029 3 30.0351 29.1263 30.6534 4 29.7486 29.2430 30.1685 5 29.9222 30.7148 29.6528 6 30.0954 30.3141 30.3794 7 29.6892 30.3470 28.9059 8 29.9410 30.4285 31.3323 9 30.4920 30.0219 30.0230 10 29.6655 30.0445 30.1254 Accuracy (rms) 0.253 0.559 0.650

[0111] Table 2: Carrier phase tracking error statistics table for scenario two

[0112] Serial number Scheme 1 measurement (μs) Scheme 2 measurement (μs) Scheme 3 measurement (μs) 1 30.0532 30.0230 29.5095 2 30.0850 30.1019 29.5647 3 29.9260 30.0504 30.1350 4 29.5847 29.8129 29.6003 5 29.8091 29.9412 31.0951 6 29.9873 29.5150 29.6520 7 29.9612 30.0019 29.3562 8 30.0467 30.0078 30.6530 9 30.1489 30.1938 31.1215 10 30.0558 29.8584 29.9650 Accuracy (rms) 0.167 0.195 0.669

[0113] The test results show that for scenario one, the accuracy of scheme 1 is obviously better than that of scheme 2 and scheme 3, the accuracy of scheme 2 is slightly better than that of scheme 3, for the strong sky wave scenario like scenario one, the performance of scheme 1 is better, which is consistent with the method described in the application, and according to the method described in the application, scheme 1 will be automatically adopted to realize carrier phase tracking, thereby obtaining the optimal tracking accuracy; for scenario two, the accuracy of scheme 1 and scheme 2 is obviously better than that of scheme 3, wherein the accuracy of scheme 1 and scheme 2 is not much different, but the calculation amount of scheme 2 is smaller, considering the calculation amount and other factors, for the non-strong sky wave scenario like scenario two, scheme 2 has better comprehensive advantages, which is consistent with the method described in the application, and according to the method described in the application, scheme 2 will be automatically adopted to realize carrier phase tracking, thereby obtaining better comprehensive tracking performance. It can be seen that the method described in the application can meet the carrier phase tracking requirement under the influence of sky wave interference, and the method described in the application is better than the current traditional method, and the comprehensive performance of the method described in the application is optimal in different scenarios.

[0114] When the method of the application is applied to a digital system, a functional block diagram is as shown in Figure 3 The main functions include an ADC sampling module, a digital wave trap module, an FIR digital band-pass filter module, an automatic search and capture and chain identification module, a sky wave and ground wave separation module, an integration interval and phase discrimination correction value calculation module, and a carrier phase tracking loop module.

[0115] The ADC sampling module is used to convert the Loran-C analog signal into a digital signal, and preferably, the ADC sampling module adopts a 16-bit ADC with a sampling frequency of 1MHz;

[0116] The digital wave trap module is used to remove continuous wave interference;

[0117] The FIR digital band-pass filter module is used to suppress signals outside the passband range, and the selected passband is 80kHz-120kHz, and the FIR filter is realized by using a 127-order Hanning window;

[0118] The automatic search and capture and chain identification module is used to search and capture the Loran-C signal of the target station;

[0119] The sky wave and ground wave separation module is used to identify the amplitude ratio and relative time delay of sky wave and ground wave, as well as the approximate position of sky wave and ground wave, and preferably, the sky wave and ground wave separation module is realized by using the IFFT method;

[0120] The integration interval and phase discrimination correction value calculation module is used to determine the integration interval of the in-phase branch and the quadrature branch of the carrier phase tracking loop, and mainly performs the functions of multi-period averaging of the sky wave and ground wave separation result, integration interval calculation, and phase discrimination correction value calculation;

[0121] The carrier phase tracking loop module adopts a Loran-C carrier phase tracking method considering sky wave interference influence, and is used for realizing carrier phase tracking of the Loran-C signal, and mainly comprises a multiplier, a digital LPF, an accumulator, a digital phase discriminator, an adder, a digital loop filter, a DDS module and a ROM module.

[0122] Preferably, the low-pass cutoff frequency of the digital LPF is designed as 10 kHz; the digital phase discriminator adopts a four-quadrant arctangent phase discriminator; the digital loop filter adopts a second-order digital Costas loop; the DDS module is used for generating a direct digital synthesis sine signal according to a frequency control word; and the ROM is a digital storage, used for storing a sine table and a cosine table.

[0123] The examples of the present application are only specific examples for the convenience of understanding, and other examples formed according to the main method or the variation of the present application all belong to the scope of the present application. In particular, since the eLoran system is inherited from the Loran-C system, the pulse signal forms of the two systems are the same, and therefore the present application can be directly applied to the eLoran system.

[0124] In the several embodiments provided in the present application, it should be understood that the disclosed device and method can be implemented in other ways. For example, the device embodiments described above are only schematic. The division of the modules or units is only a logical function division. There can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another device, or some features can be ignored or not executed.

[0125] The units can or can not be physically separate, and the components shown as units can be one physical unit or multiple physical units, that is, can be located in one place, or can be distributed to multiple different places. According to actual needs, part or all of the units can be selected to achieve the purpose of the embodiment scheme.

[0126] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present alone, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0127] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application essentially or say the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product. The software product is stored in a storage medium, including a plurality of instructions to make a device (which can be a single-chip microcomputer, a chip, etc.) or a processor execute all or part of the steps of the method described in various embodiments of the present application. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (Read-Only Memory, ROM), a random access memory (Random Access Memory, RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0128] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any change or replacement within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A Loran-C carrier phase tracking method and system considering skywave interference, characterized in that, The method comprises the steps of: obtaining the amplitude ratio and time delay difference of the sky wave and ground wave by using the sky-ground wave separation technology, and determining whether the sky wave is strong according to the amplitude ratio of the sky wave and ground wave; The phase discrimination correction number is calculated based on the amplitude ratio and time delay difference of the sky wave and ground wave, and an integral interval A of the in-phase branch and quadrature branch signals of the carrier phase tracking loop is determined, wherein the phase discrimination correction number The calculation of the phase discrimination correction number includes: , wherein, represents the carrier angular frequency of the Loran C signal, represents a threshold of a strong sky wave, represents a time delay difference, represents a four-quadrant inverse tangent operator; SGR is the amplitude ratio of the sky wave and ground wave, and SGR is taken as a critical point, if , it is non-strong sky wave interference, if , it is strong sky wave interference; integrating the in-phase branch signal and quadrature branch signal according to the integral interval A, and calculating the phase discrimination result, and correcting the phase discrimination result to obtain the phase discrimination correction value; adjusting the local carrier based on the phase discrimination correction value to realize the carrier phase tracking.

2. The Loran-C carrier phase tracking method with consideration of skywave interference influence according to claim 1, characterized in that: The obtaining of the amplitude ratio and time delay difference of the sky wave and ground wave comprises the steps of: In the sky-ground wave separation module, the sky-ground wave separation technology is used to realize the sky-ground wave identification of Loran-C signal, and the amplitude ratio SGR and time delay difference of sky wave and ground wave are obtained ; The sky-ground wave separation technology uses the frequency spectrum division method.

3. The method for tracking Loran-C carrier phase with consideration of skywave interference influence according to claim 1 or 2, characterized in that: The determination of the strong sky wave comprises the steps of: setting a threshold value, when the amplitude ratio SGR of the sky wave and ground wave is greater than the threshold value, the sky wave is strong, and when the amplitude ratio SGR of the sky wave and ground wave is not greater than the threshold value, the sky wave is not strong.

4. The Loran-C carrier phase tracking method with consideration of skywave interference influence according to claim 1, characterized in that: The determination of the integral interval A comprises the steps of: The in-phase and quadrature branches adopt the same integration interval, and the amplitude ratio SGR of the sky wave and the ground wave and the strong sky wave threshold are determined according to the amplitude ratio SGR of the sky wave and the ground wave determine the integration interval A; The calculation of the integration interval A comprises, ,, wherein , respectively define upper and lower limits of an integration interval for a ground wave signal within a Loran-C pulse signal, denotes the length of the pulse signal in time, denotes the start time of the current Loran-C pulse signal.

5. The Loran-C carrier phase tracking method with consideration of skywave interference influence according to claim 4, characterized in that: The obtaining of the phase discrimination result comprises the steps of: The carrier phase tracking loop adopts a Costas loop structure, the Loran-C signal is multiplied by a sine carrier and a cosine carrier respectively, and in-phase branch signals and quadrature branch signals are obtained through low-pass filter (LPF) filtering According to the integral interval A, the integral results of the in-phase and quadrature branches of each GRI period reference pulse signal are The integral results of the in-phase and quadrature branches are sent into a phase discriminator, and a phase discrimination result is output .​​​​​ 6. The Loran-C carrier phase tracking method with consideration of skywave interference influence according to claim 5, characterized in that: The phase identification result The calculation includes, ， wherein, denotes a four-quadrant arctangent operator, denotes the integration result of the in-phase branch, denotes the integration result of the quadrature branch.

7. The Loran-C carrier phase tracking method with consideration of skywave interference influence according to claim 6, characterized in that: The calculation of the phase discrimination correction value comprises the steps of: based on the phase detection result and the phase detection correction number , calculate the phase detection correction value; ， wherein denotes a phase detection correction value.

8. The Loran-C carrier phase tracking method with consideration of skywave interference according to any one of claims 1-2, 4-7, characterized in that: The adjustment of the local carrier comprises the steps of: said phase correction value The loop filter of the Costas carrier phase tracking loop calculates the frequency control word and adjusts the VCO output frequency and thus the local carrier signal.

9. A Loran-C carrier phase tracking system with skywave interference consideration, characterized by, The method comprises the steps of: a data acquisition unit, configured to obtain the amplitude ratio and time delay difference of the sky wave and ground wave by using the sky-ground wave separation technology; a determination module, configured to determine whether the sky wave is strong according to the amplitude ratio of the sky wave and ground wave; a calculation module, configured to calculate the phase discrimination correction value based on the amplitude ratio and time delay difference of the sky wave and ground wave, and determine the integral interval A of the carrier phase tracking loop in-phase branch signal and quadrature branch signal; Integrate the in-phase branch signal and the quadrature branch signal according to the integration interval A, calculate the phase detection result, and correct the phase detection result to obtain the phase detection correction value, wherein the phase detection correction value is... The calculations include: ,in, This indicates the carrier angular frequency of the Loran-C signal. This indicates the threshold for strong skywave. Indicates the time delay difference. This represents the four-quadrant arctangent operator; SGR is the amplitude ratio of the sky wave to the ground wave, with SGR as... Time is used as a critical point, if If it is a non-strong skywave interference, then it is a non-strong skywave interference. This would be strong skywave interference; an adjustment module, configured to adjust the local carrier based on the phase discrimination correction value to realize the carrier phase tracking.

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