A method and device for predicting the time delay of a Loran sky wave passing through the ionosphere based on a cosine model

Abstract

The present invention discloses a method and device for predicting the time delay of a Roland skywave signal passing through the ionosphere based on a cosine model. The method comprises constructing a first cosine model according to the actual measured time delay of the Roland skywave passing through the ionosphere in combination with a mathematical method, wherein the first parameter in the first cosine model comprises a phase, an amplitude, a period and a DC constant term; determining a first parameter value of the first cosine model; and predicting the ionosphere time delay of the Roland skywave using a second cosine model, wherein the second cosine model is a model obtained by substituting the first parameter value into the first cosine model. The method for predicting the time delay of the Roland skywave through the ionosphere of the scheme of the present invention is simple, effective and has high accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of ground-based long-wave wireless navigation, and in particular relates to a method and device for predicting the time delay of a Loran sky wave passing through an ionosphere based on a cosine model. Background Art

[0002] Loran is the abbreviation of long-distance wireless navigation system. It was invented in the 1960s and is currently used as a backup system for the global satellite navigation system. In recent years, with the development of modern digital signal processing technology and antenna transceiver technology, the application of Loran sky waves with longer transmission distances has become possible. However, since the propagation path of Loran sky waves is reflected by the ionosphere, and the characteristics of the ionosphere are complex and uncertain, the resulting delay is difficult to predict.

[0003] The traditional method of calculating the time delay of Roland skywave passing through the ionosphere is based on electromagnetic principles and is calculated using analytical or numerical methods. Since the calculation steps are cumbersome and involve a large number of parameters, and the large number of ionosphere parameters change irregularly and cannot be accurately given, the calculation tends to be theoretical simulation and is difficult to apply in practice. Summary of the invention

[0004] The present invention provides a method and device for predicting the time delay of a Loran skywave passing through the ionosphere based on a cosine model. Based on the measured cosine model, the time delay generated by the Loran skywave passing through the ionosphere during propagation can be predicted. The method is simple, clear and easy to calculate, and the accuracy of the prediction of the time delay of a Loran skywave signal passing through the ionosphere can be improved.

[0005] In a first aspect, a method for predicting the time delay of a Roland sky wave passing through the ionosphere based on a cosine model is provided, which is specifically implemented according to the following steps:

[0006] Step 1: construct a cosine model based on the actual measured time delay of the Loran sky wave passing through the ionosphere and combine mathematical methods to analyze the cosine model parameters;

[0007] Step 2, calculating the phase parameters of the cosine model;

[0008] Step 3, calculate the amplitude and period parameters of the cosine model;

[0009] Step 4: Substitute all parameters into the cosine model to calculate and predict the time delay of the Loran sky wave passing through the ionosphere.

[0010] The present invention is also characterized in that step 1 is specifically implemented according to the following steps:

[0011] Step 1.1: Measurement of the time delay of the Loran sky wave through the ionosphere Figure 1As shown. The GNSS receiver and the Loran receiver receive signals through their respective receiving antennas. One of the timing GNSS receivers provides a time reference for the measurement. Its standard second pulse signal is compared with the pulse period signal output by the Loran receiver through a counter. The difference minus the theoretical propagation delay is the actual measured delay of the sky wave passing through the ionosphere.

[0012] Step 1.2, the cosine model contains four parameters: the DC constant term, the amplitude, phase and period of the cosine function. The DC constant term is highly correlated with the equivalent reflection of the ionosphere during the calculation process. Since the signal frequency is determined, the DC constant can be set to 25, in microseconds.

[0013] To calculate the phase parameters of the cosine model in step 2, the time information of the reflection point needs to be known. The time information is related to the position coordinates of the reflection point. The specific implementation is as follows:

[0014] Step 2.1, the ionospheric reflection point is the middle position of the sky wave propagation path. Although the earth is not a regular sphere, due to its small eccentricity and the fact that the total amount of ionospheric electrons is distributed the same within a certain distance range, the longitude and latitude coordinates of the reflection point between the sending and receiving points can be calculated based on this. and λ m , the formula is as follows:

[0015]

[0016] In formula (1), and λ s are the latitude and longitude coordinates of the transmitting station, and λ r are the latitude and longitude coordinates of the receiving point, respectively, and the coordinates are all positive in the northern hemisphere and east longitude;

[0017] Step 2.2: The phase information of the cosine model is related to the local time and the geographical noon time. The message content extracted from the received Loran signal contains the time information of the Universal Coordinated Time. Combined with the position longitude of the ionospheric reflection point calculated in step 2.1, the local time near the reflection point and the geographical noon time can be calculated. The local time t near the reflection point is:

[0018]

[0019] In formula (2), UTC is the world coordinated time demodulated from the Loran signal modulation message. If the calculated result is greater than 86400 seconds, 86400 can be subtracted to keep the result in seconds between 0 and 24 hours.

[0020] my country's geographical time zone is East 8, corresponding to the longitude of 120°. The earth rotates once in about 1440 minutes (the error is very small and can be ignored), corresponding to a rotation of 1° every four minutes. The formula for calculating the geographical noon time τ at the location is:

[0021] τ=(120-λ m )×4×60+43200 (3)

[0022] The amplitude and period parameters to be calculated in step 3 are a set of polynomial coefficients used to represent the ionospheric coefficients. They are the amplitude and period polynomial coefficients obtained by fitting based on the measured ionospheric delay information. They reflect the ionospheric variation characteristics at the current time and place, and are implemented in the following steps:

[0023] Step 3.1. The geomagnetic North Pole is the point on the Earth's surface where the magnetic field is pointing vertically downward. Its position moves over time and is different from the geographically defined North Pole. The total number of electrons in the characteristics of the ionosphere is usually related to the geomagnetic coordinates. It is necessary to convert the geographic reflection point coordinates into the geomagnetic reflection point coordinates. Then the geomagnetic latitude φ can be expressed as:

[0024]

[0025] In formula (4), φ p and λ p are the geomagnetic reference latitude and longitude, with values ​​of 78.3° and 291° respectively;

[0026] Step 3.2, polynomial coefficient fitting is based on the data of accurate measurement of ionospheric delay by differential method using GNSS receiving equipment as the benchmark, and then the amplitude and period coefficients of the cosine model are fitted using software tools such as Matlab;

[0027] Step 3.3, the ionosphere changes steadily at night, which can be expressed by a DC constant. However, the ionosphere as a whole changes with the seasons. In summer, the daytime is long, and the propagation delay is small when the night is stable. In winter, the daytime is short, and the propagation delay is large when the night is stable. Therefore, it is necessary to add a seasonal factor for auxiliary calculation. The seasonal factor ensures that the model is more accurate by correcting the DC constant. It is calculated during software fitting in the same way as step 3.2.

[0028] The final Loran skywave ionospheric delay prediction formula in step 4 is:

[0029]

[0030] In formula (5),

[0031]

[0032]

[0033] α n and β n Respectively represent the amplitude polynomial coefficient and period polynomial coefficient of the cosine model, F d and F n They represent the seasonal factors for the daytime and nighttime periods respectively, and φ is the geomagnetic latitude.

[0034] In the second aspect, a device for predicting the time delay of a Roland skywave passing through the ionosphere based on a cosine model is provided, comprising: a processor for constructing a first cosine model based on the actually measured time delay of the Roland skywave passing through the ionosphere in combination with a mathematical method, wherein the first parameter in the first cosine model includes a phase, an amplitude, a period, and a DC constant term; determining the first parameter value of the first cosine model; and predicting the ionosphere time delay of the Roland skywave using a second cosine model, wherein the second cosine model is a model obtained by substituting the first parameter value into the first cosine model. The processor can perform the corresponding functions in the method example of the first aspect above, and specifically refer to the detailed description in the method example, which will not be repeated here.

[0035] According to a third aspect, a computer-readable storage medium is provided for storing a computer program, wherein the computer program includes instructions for executing the method in the first aspect or any possible implementation of the first aspect.

[0036] The beneficial effect of the present invention is that a cosine model is constructed through the variation law of the ionosphere and the measured signal delay data, and the parameters reflecting the ionosphere propagation characteristics are fitted into the model coefficients, which is simple, clear and easy to calculate, and greatly improves the accuracy of the prediction of the time delay of the Roland skywave signal through the ionosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural block diagram of actual time delay measurement in a method for predicting time delay of a Loran sky wave passing through the ionosphere based on a cosine model of the present invention;

[0038] Figure 2 It is a monthly average value of the time delay of the sky wave passing through the ionosphere calculated and measured by a GNSS timing receiver and a Loran receiver in a method for predicting the time delay of the Loran sky wave passing through the ionosphere based on a cosine model of the present invention;

[0039] Figure 3 This is the error result diagram comparing the delay value predicted by the cosine model in different time periods with the actual measured value.

[0040] Figure 4 It is a schematic diagram of a device for predicting the time delay of a Loran sky wave passing through the ionosphere based on a cosine model provided by the present invention. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] Unless otherwise specified, all technical and scientific terms used in the embodiments of the present application have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit the scope of this application.

[0043] The terms "first", "second", "third", etc. in the description and claims of the present invention are used to distinguish different objects rather than to limit a specific order.

[0044] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0045] The present invention provides a Loran skywave delay prediction method based on a cosine model, which is specifically implemented according to the following steps:

[0046] Step 1: Construct a cosine model based on the actual measured time delay of the Loran skywave passing through the ionosphere and mathematical methods:

[0047] Step 1.1, the Global Navigation Satellite System (GNSS) receiver and the Loran receiver receive signals through their respective receiving antennas. One of the timing GNSS receivers provides a time reference for the measurement. Its standard second pulse signal is compared with the pulse period signal output by the Loran receiver through a counter. The difference minus the theoretical propagation delay is the actual measured delay of the sky wave passing through the ionosphere.

[0048] Step 2: Calculate the phase parameters of the cosine model:

[0049] Step 2.1, the ionospheric reflection point is the middle position of the sky wave propagation path. Although the earth is not a regular sphere, due to its small eccentricity and the fact that the total amount of ionospheric electrons is distributed the same within a certain distance range, the latitude coordinates of the reflection point between the sending and receiving points can be calculated based on this. and longitude coordinate λ m , the formula is as follows:

[0050]

[0051] in, is the latitude coordinate of the transmitting station, λ sis the longitude coordinate of the transmitting station, is the latitude coordinate of the receiving point, λ r is the longitude coordinate of the receiving point.

[0052] It should be noted that the coordinates in the present invention are all positive in the northern hemisphere and east longitude.

[0053] Step 2.2: The phase information of the cosine model is related to the local time and the geographical noon time. Combined with the position longitude of the ionospheric reflection point calculated in step 2.1, the local time and geographical noon time near the reflection point can be calculated. The local time t near the reflection point is:

[0054]

[0055] Among them, the Universal Time Coordinated (UTC) is demodulated from the Loran signal modulation message.

[0056] In the above formula (2), if the calculated result is greater than 86400 seconds, just subtract 86400 to keep the result in seconds between 0 and 24 hours.

[0057] my country's geographical time zone is East 8, corresponding to the longitude of 120°. The earth rotates once in about 1440 minutes (the error is very small and can be ignored), corresponding to a rotation of 1° every four minutes. The formula for calculating the geographical noon time τ at the location is:

[0058] τ=(120-λ m )×4×60+43200 (3)

[0059] Step 3: Calculate the amplitude and period parameters of the cosine model:

[0060] Step 3.1. The geomagnetic North Pole is the point on the Earth's surface where the magnetic field is pointing vertically downward. Its position moves over time and is different from the geographically defined North Pole. The total number of electrons in the characteristics of the ionosphere is usually related to the geomagnetic coordinates. It is necessary to convert the geographic reflection point coordinates into the geomagnetic reflection point coordinates. Then the geomagnetic latitude φ can be expressed as:

[0061]

[0062] Among them, φ p is the geomagnetic reference latitude, which is 78.3°; p It is the geomagnetic reference longitude, and its value is 291°.

[0063] Step 3.2, polynomial coefficient fitting is based on the data of accurate measurement of ionospheric delay by differential method using GNSS receiving equipment, and then the amplitude and period coefficients of the cosine model are fitted using software tools such as Matlab.

[0064] Step 3.3, the ionosphere changes steadily at night, which can be expressed by a DC constant. However, the ionosphere as a whole changes with the seasons. In summer, the daytime is long, and the propagation delay is small when the night is stable. In winter, the daytime is short, and the propagation delay is large when the night is stable. Therefore, it is necessary to add a seasonal factor for auxiliary calculation. The seasonal factor ensures that the model is more accurate by correcting the DC constant. It is calculated during software fitting in the same way as step 3.2.

[0065] Step 4: Substitute all parameters into the cosine model to calculate and predict the time delay of the Roland sky wave passing through the ionosphere:

[0066]

[0067] in,

[0068]

[0069]

[0070] α n represents the amplitude polynomial coefficient of the cosine model, β n Represents the periodic polynomial coefficients of the cosine model; F d represents the seasonal factor for the daytime period, F n represents the seasonal factor of the night period, and φ is the geomagnetic latitude.

[0071] Exemplarily, the following is described in conjunction with a specific embodiment, and can be implemented according to the following steps:

[0072] Step 1: Calculate the measured time delay of the Loran skywave signal through the ionosphere using the GNSS receiver and the Loran receiver. Figure 3 As shown;

[0073] Step 2: According to the coordinates of the launch point Receiving point coordinates The coordinates of the reflection point are calculated by the above formula (1): According to the coordinates of the reflection point and the above formula (3), the local noon geographic time τ = 46043.184s is calculated;

[0074] Step 3: Calculate the geomagnetic latitude φ=16.7895° using the above formula (4); then use the Matlab software fitting tool to fit the cosine model amplitude and period, and calculate A using the above formulas (6) and (7):m =-1.742e-05, T=1.335e+05, Fd=6.52e-06, Fn=1.26e-06;

[0075] Step 4: The above formula (5) can be used to predict the time delay of the Loran sky wave passing through the ionosphere.

[0076] like Figure 3 The figure shows the error results of the delay values ​​predicted by the cosine model in different time periods compared with the actual measured values. Figure 3 (a) in the figure shows the error result diagram during the stable period of daytime. Figure 3 (b) in the figure shows the error result diagram during the stable period at night.

[0077] When the receiving time is at night or during the daytime when the sun does not rise or set, the error of the sky wave delay estimated by the model is stable within 1 μs compared with the actual measured value. It can be found that the method for predicting the time delay of the Loran sky wave passing through the ionosphere based on the cosine model of the present invention is simple to use and has high accuracy.

[0078] Combination of the above Figure 1-Figure 3 , describes the method embodiment of the present application in detail, and the following is combined with Figure 4 , describing the device embodiments of the present application, the device embodiments correspond to the method embodiments, so the parts that are not described in detail can refer to the method embodiments in the previous parts.

[0079] Figure 4 An embodiment of the present application provides a device 400 for predicting the time delay of a Loran sky wave passing through the ionosphere based on a cosine model. The device 400 may include a processor 410.

[0080] Processor 410, configured to construct a first cosine model according to the actually measured time delay of the Loran sky wave passing through the ionosphere in combination with a mathematical method, wherein the first parameters in the first cosine model include a phase, an amplitude, a period, and a DC constant term;

[0081] Determining a first parameter value of the first cosine model;

[0082] The ionospheric delay of the Roland sky wave is predicted by using a second cosine model, where the second cosine model is a model obtained by substituting the first parameter value into the first cosine model.

[0083] Optionally, in some embodiments, the processor 410 is further configured to:

[0084] Using a global satellite navigation and positioning system GNSS receiver and a Loran receiver to receive signals through respective receiving antennas, wherein the GNSS receiver provides a time reference for measurement;

[0085] Calculate the standard second pulse signal of the GNSS receiver and the pulse period signal output by the Loran receiver respectively according to the received signal;

[0086] Calculating the difference between the standard second pulse signal of the GNSS receiver and the pulse period signal output by the Loran receiver;

[0087] Subtracting the difference from the theoretical propagation delay to obtain the actually measured delay of the Loran sky wave passing through the ionosphere;

[0088] The first parameter value is determined according to the ionospheric delay.

[0089] Optionally, in some embodiments, the processor 410 is further configured to: determine the first parameter value according to the following formula:

[0090]

[0091] Among them, τ iono represents the ionospheric delay, A m is the amplitude, T is the period, τ is the phase, 25 is the DC constant term, F d represents the seasonal factor for the daytime period, F n Indicates the seasonal factor for night time.

[0092] Optionally, in some embodiments, the Said The α n and β n are the amplitude polynomial coefficient and period polynomial coefficient obtained by fitting according to the measured ionospheric time delay information, and φ is the geomagnetic latitude.

[0093] It should be understood that the processor of the embodiment of the present application may be an integrated circuit image processing system with signal processing capabilities. In the implementation process, each step of the above method embodiment can be completed by an integrated logic circuit of hardware in the processor or an instruction in the form of software. The above processor can be a general-purpose processor, a digital signal processor (Digital Signal Processor, DSP), an application-specific integrated circuit (Application Specific Integrated Circuit, ASIC), a field programmable gate array (Field Programmable Gate Array, FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The disclosed methods, steps and logic block diagrams in the embodiments of the present application can be implemented or executed. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc.

[0094] An embodiment of the present application also provides a computer-readable storage medium for storing a computer program.

[0095] Optionally, the computer-readable storage medium can be applied to the device for predicting the time delay of a Roland skywave passing through the ionosphere based on a cosine model in the embodiments of the present application, and the computer program enables the computer to execute the corresponding processes implemented by the device for predicting the time delay of a Roland skywave passing through the ionosphere based on a cosine model in each method of the embodiments of the present application. For the sake of brevity, they are not repeated here.

[0096] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0097] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for predicting the time delay of a Loran sky wave passing through the ionosphere based on a cosine model, characterized in that: include: A first cosine model is constructed according to the actually measured time delay of the Loran sky wave passing through the ionosphere in combination with a mathematical method, wherein the first parameters in the first cosine model include the phase, amplitude, period and DC constant term of the cosine model; Determining a first parameter value of the first cosine model; Predicting the ionospheric delay of the Roland sky wave by using a second cosine model, wherein the second cosine model is a model obtained by substituting the first parameter value into the first cosine model; Determining the first parameter value of the first cosine model includes: using a global satellite navigation and positioning system GNSS receiver and a Loran receiver to receive signals through respective receiving antennas, wherein the GNSS receiver provides a time reference for measurement, respectively calculating a standard second pulse signal of the GNSS receiver and a pulse period signal output by the Loran receiver according to the received signals, calculating a difference between the standard second pulse signal of the GNSS receiver and the pulse period signal output by the Loran receiver, subtracting the difference from a theoretical propagation delay to obtain an actually measured time delay of the Loran sky wave passing through the ionosphere, and determining the first parameter value according to the ionosphere delay; Determining the first parameter value according to the ionospheric time delay includes bringing all parameters into a cosine model for calculation to predict the time delay of the Roland sky wave passing through the ionosphere; Among them, τ iono represents the ionospheric delay, A m is the amplitude, T is the period, τ is the geographical noon time of the location, 25 is the DC constant term, F d represents the seasonal factor for the daytime period, F n Indicates the seasonal factor for night time.

2. The method according to claim 1, characterized in that: Said Said The α n and β n are the amplitude polynomial coefficient and period polynomial coefficient obtained by fitting according to the measured ionospheric time delay information, and φ is the geomagnetic latitude.

3. A device for predicting the time delay of a Loran sky wave passing through the ionosphere based on a cosine model, characterized in that: include: A processor, configured to construct a first cosine model according to the actually measured time delay of the Loran skywave passing through the ionosphere in combination with a mathematical method, wherein the first parameters in the first cosine model include a phase, an amplitude, a period, and a DC constant term; The processor is further configured to receive signals using a global satellite navigation and positioning system GNSS receiver and a Loran receiver through respective receiving antennas, wherein the GNSS receiver provides a time reference for measurement; Calculate the standard second pulse signal of the GNSS receiver and the pulse period signal output by the Loran receiver respectively according to the received signal; Calculating the difference between the standard second pulse signal of the GNSS receiver and the pulse period signal output by the Loran receiver; Subtracting the difference from the theoretical propagation delay to obtain the actually measured delay of the Loran sky wave passing through the ionosphere; determining the first parameter value according to the ionosphere delay; The processor is further used to bring all parameters into the cosine model to calculate and predict the time delay of the Loran sky wave passing through the ionosphere; Among them, τ iono represents the ionospheric delay, A m is the amplitude, T is the period, τ is the geographical noon time of the location, 25 is the DC constant term, F d represents the seasonal factor for the daytime period, F n Indicates the seasonal factor for night time.

4. The device according to claim 3, characterized in that Said Said The α n and β n are the amplitude polynomial coefficient and period polynomial coefficient obtained by fitting according to the measured ionospheric time delay information, and φ is the geomagnetic latitude.

5. A computer-readable storage medium, characterized in that: The method comprises instructions for executing the method for predicting the time delay of a Loran sky wave passing through the ionosphere based on a cosine model as described in any one of claims 1 to 2.

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