CN113992287B - Low-frequency time code time service signal carrier frequency selection method and system - Google Patents
Low-frequency time code time service signal carrier frequency selection method and system Download PDFInfo
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Abstract
The invention discloses a carrier frequency selection method and a system for a low-frequency time code time service signal, wherein the method comprises the following steps: performing frequency point first screening based on a preset antenna effective radiation power threshold value to obtain a first screening result; performing frequency point secondary screening based on in-band interference factors to obtain a secondary screening result; performing third screening of frequency points based on the world wave interference characteristic factors to obtain a third screening result; and based on the first screening result, the second screening result and the third screening result, screening according to frequency generation factors to obtain a final screening result, and completing the optimization of the carrier frequency of the low-frequency time code time service signal. The method can select the carrier frequency of the low-frequency time code time service signal meeting the preset requirement.
Description
Technical Field
The invention belongs to the technical field of radio communication and electric wave propagation, and particularly relates to a carrier frequency selection method and system for a low-frequency time code time service signal.
Background
The range of the low-frequency band wave is 30-300 kHz, which is about one hundred parts per billion of the whole frequency spectrum resource. Compared with other frequency bands, the low-frequency radio wave propagation characteristics have some unique characteristics, and the propagation of the low-frequency radio wave mainly depends on ground wave and ionospheric reflection (sky wave signals); the ground wave propagation channel can be regarded as a linear matching network, and the attenuation of the field intensity and the change of the phase position are very slow after the signal passes through the channel; sky wave signals formed by ionospheric reflections can receive low frequency signals over significant distances (illustratively,. Gtoreq.2000 km). Because the low-frequency radio wave has the characteristics of stable transmission, wide effective coverage range, strong permeability and the like, the low-frequency radio wave has been successfully applied to the propagation of low-frequency time code signals in all countries of the world, and is increasingly more widely regarded.
At present, frequency points used by each low-frequency time code station internationally comprise 40kHz, 60kHz, 68.5kHz, 77.5kHz and the like; the transmitting frequency is one of core parameters of the low-frequency time code time service system, and the selection of the transmitting frequency directly influences the design of the transmitting system and simultaneously influences the space propagation characteristic of a time code signal and the receiving characteristic of a receiver. Therefore, a systematic low-frequency band frequency selection method needs to be formed in the early stage of the construction of the low-frequency time code time service station, so that technical support is provided for the construction of the station.
Today, when creating multiple low frequency time code stations, it is necessary to consider reselecting the carrier frequency of the new station; as various electronic devices, particularly charging devices, power supplies and other devices, rapidly develop over the years, low-frequency electromagnetic waves are generated, which makes the electromagnetic environment more complex; in addition, the new station generally expands the information quantity, further improves the time service precision, and all the factors can put more strict requirements on the low-frequency time code signal transmission quality, and further put more requirements on the key parameter of the carrier frequency, so that the prior method according to engineering experience and technical discussion cannot be suitable for the carrier frequency selection of the current low-frequency time code time service signal. Illustratively, in 2007, when a low-frequency code station of the BPC is constructed, the carrier frequency is selected to be 68.5kHz, and the selection of the frequency point is mainly based on engineering experience and technical discussion.
Because the current frequency point selection needs to consider geographic parameters and population distribution, multiple factors such as seasonal variation, frequency synthesis and the like are synthesized, and the existing low-frequency-band broadcasting station frequency point nearby the station needs to be avoided; in addition, the research work on low-frequency optimization at present does not form a system, and a large blank exists in the technology. In summary, it is highly desirable to provide a new method of optimizing the frequency of a low frequency time code signal.
Disclosure of Invention
The invention aims to provide a method and a system for selecting carrier frequencies of low-frequency time-code time service signals, which are used for solving one or more of the technical problems. The method can select the carrier frequency of the low-frequency time code time service signal meeting the preset requirement.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention discloses a carrier frequency selection method of a low-frequency time code time service signal, which comprises the following steps:
performing frequency point first screening based on a preset antenna effective radiation power threshold value to obtain a first screening result;
Performing frequency point secondary screening based on in-band interference factors to obtain a secondary screening result;
Performing third screening of frequency points based on the world wave interference characteristic factors to obtain a third screening result;
And based on the first screening result, the second screening result and the third screening result, screening according to frequency generation factors to obtain a final screening result, and completing the optimization of the carrier frequency of the low-frequency time code time service signal.
The invention further improves that the frequency point is screened for the first time based on the preset antenna effective radiation power threshold value, and the step of obtaining the first screening result specifically comprises the following steps:
Based on a preset antenna effective radiation power threshold value, calculating and obtaining a minimum value of frequency according to an empirical formula;
wherein the expression of the empirical formula is that,
Wherein P r is the radiation power; v t is the voltage of the effective top cap of the antenna; c is a capacitor; h e is the antenna effective height; f is the frequency of the broadcast.
The invention further improves that the step of carrying out the second screening of the frequency points based on the in-band interference factors specifically comprises the following steps:
Eliminating a preset known low-frequency station frequency point;
determining a test point, performing atmospheric noise test on a preset distance area of the test point, and eliminating frequency points with a test field intensity result larger than a preset threshold value.
The invention further improves that the frequency points are screened for the third time based on the interference characteristic factors of the sky and earth waves, and the step of obtaining the third screening result comprises the following steps:
Calculating the field intensity distribution characteristics of the sky-earth waves of different frequency points according to the space-earth wave interference distribution estimation model to obtain an estimation result of the low-frequency space-earth wave interference field intensity;
and based on the estimation result of the low-frequency space-earth wave interference field intensity, carrying out low-frequency point screening by combining field intensity fading factors, seasonal variation factors and population coverage factors to obtain a third screening result.
The invention further improves that the step of calculating the field intensity distribution characteristics of the sky-earth waves of different frequency points according to the space-earth wave interference distribution estimation model to obtain the estimation result of the low-frequency space-earth wave interference field intensity specifically comprises the following steps:
The propagation field strength of the ground wave signal is expressed as E (dB) =109.54+20lgw—20lgd+10lgp Σ;
Wherein d-is the great circle distance between the receiving point and the transmitting point; w is the ground wave attenuation parameter; p Σ -transmit antenna radiation power;
the phase difference of the world wave is expressed as,
Wherein fix () represents rounding; t is the period of transmitting electromagnetic waves; the propagation time difference between the one-jump sky wave and the earth surface is t 0 = (s-d)/c; the propagation path of the one-hop sky wave is s=2s 1;
s 1＝r2+(r+h)2 -2r (r+h) cos α; wherein r is the earth radius; h is the ionization layer height;
d <1000 km: e Total (S) (d)＝|E Ground wave (d) +512·sin (θ+90) |;
d is more than or equal to 1000 km: e Total (S) (d)＝|E Ground wave (d)+E Ground wave sin (θ+90) |;
Where E Total (S) represents an estimated value of the superimposed field strength of the sky-ground wave, and E Ground wave represents an estimated value of the field strength of the ground wave.
The invention further improves that the step of screening the low-frequency points based on the estimation result of the low-frequency space-earth wave interference field intensity and combining the field intensity fading factor, the seasonal variation factor and the population coverage factor to obtain the third screening result specifically comprises the following steps:
① Setting a minimum field intensity threshold E min and a distance range threshold Deltad lower than a decay region corresponding to E min when field intensity fading factors are combined, and screening frequency points with reserved distance ranges lower than Deltad;
② When seasonal variation factors are combined, calculating to obtain the distribution of field intensity of each frequency point along with distance in winter and summer, and comparing the obtained differences of the distribution in winter and summer; setting a correlation threshold based on the difference, and screening frequency points with retained correlation larger than the correlation threshold;
③ And when the population coverage factors are combined, setting a population estimation value threshold of the subsidence area according to the preset user group demand of the station, and screening and reserving frequency points of which the population estimation value of the subsidence area is lower than the population estimation value threshold of the subsidence area.
The invention further improves that the steps for selecting according to the frequency generation factors to obtain the final screening result based on the first screening result, the second screening result and the third screening result, and completing the optimization of the carrier frequency of the low-frequency time code time service signal specifically comprise the following steps:
and based on the first screening result, the second screening result and the third screening result, adopting integer frequency division of the reference frequency generated by the atomic clock in the low frequency band as a screening result.
The invention relates to a carrier frequency selection system of a low-frequency time code time service signal, which comprises:
The first screening module is used for carrying out frequency point first screening based on a preset antenna effective radiation power threshold value to obtain a first screening result;
the second screening module is used for carrying out frequency point second screening based on in-band interference factors to obtain a second screening result;
The third screening module is used for carrying out third screening on the frequency points based on the world wave interference characteristic factors to obtain a third screening result;
and the result acquisition module is used for screening according to the frequency generation factors based on the first screening result, the second screening result and the third screening result to obtain a final screening result, and completing the optimization of the carrier frequency of the low-frequency time code time service signal.
Compared with the prior art, the invention has the following beneficial effects:
the method can select the carrier frequency of the low-frequency time code time service signal meeting the preset requirement.
In the method disclosed by the invention, analysis is performed from three angles of signal transmission, signal transmission and signal reception, and various factors such as geographic environment, atmospheric parameters, population distribution and the like are integrated, so that a specific low-frequency time code time service signal frequency selection method is provided. Specifically, the invention is set up aiming at a low-frequency time code transmitting and broadcasting system, and provides a frequency selection method of a low-frequency time code time service signal.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description of the embodiments or the drawings used in the description of the prior art will make a brief description; it will be apparent to those of ordinary skill in the art that the drawings in the following description are of some embodiments of the invention and that other drawings may be derived from them without undue effort.
Fig. 1 is a flow chart of a method for selecting carrier frequency of a low-frequency time-code time service signal according to an embodiment of the invention;
Fig. 2 is a schematic diagram of an estimation of a phase difference of an earth wave according to an embodiment of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the attached drawing figures:
the embodiment of the invention discloses a carrier frequency selection method of a low-frequency time code time service signal, which specifically comprises the following steps:
(1) First screening: and screening frequency points according to the set antenna effective radiation power threshold value.
(2) Second screening: taking in-band interference near the broadcasting station into consideration for screening, in the screening, besides the known low-frequency station frequency points, the atmospheric noise test is required to be developed near the broadcasting station, and the frequency points with larger test field intensity results are eliminated;
(3) Third screening: and (5) taking the interference characteristic factors of the world waves into consideration to carry out frequency point screening. Firstly, calculating the field intensity distribution characteristics of the heaven-earth waves of different frequency points according to an heaven-earth wave interference distribution estimation model; and then, according to the model, combining field intensity fading factors, seasonal variation factors and population coverage factors to carry out low-frequency point screening.
(4) Fourth screening: consider a frequency generation factor. In the frequency point set screened in the previous three steps, the integer frequency division of the common reference frequency generated by the atomic clock in the low frequency band is recommended to be used as the frequency point to be selected.
The method provided by the embodiment of the invention can select the carrier frequency of the low-frequency time code time service signal meeting the preset requirement. Specifically, in the method disclosed by the invention, analysis is performed from three angles of signal transmission, signal transmission and signal reception, and various factors such as geographic environment, atmospheric parameters, population distribution and the like are integrated, so that a specific low-frequency time code time service signal frequency selection method is provided.
Referring to fig. 1, in the method for selecting carrier frequencies of low-frequency time-code time-service signals according to the embodiment of the present invention, the problem of selecting the frequencies of the low-frequency time-code time-service signals needs to be considered by integrating the whole communication link, including the steps of generating and transmitting the low-frequency signals, and receiving the user, and the method specifically includes the following steps:
(1) First screening, considering effective radiation power factor of antenna
From the viewpoint of low-frequency signal transmission, the frequency preferably needs to consider the relation between the frequency and the antenna radiation power; obviously, if this factor is considered alone, it is desirable that the antenna radiation power is as high as possible without changing other parameters of the antenna.
The radiation power of the monopole antenna with the top load has the following empirical formula:
wherein P r is the radiation power; v t is the voltage (unit: V) of the antenna effective top cap; c is capacitance (unit: F); h e is the effective height of the antenna (unit: m); f is the frequency of the transmission (unit: hz).
It can be seen from the above equation that the higher the frequency of transmission, the greater the radiation power, with the other conditions unchanged.
From the above analysis, it can be seen that the minimum value of the frequency can be calculated according to the above equation based on the actual radiation power requirement of the station construction.
(2) The second screening considers the in-band interference factors near the sending and broadcasting station
When selecting the low frequency time code working frequency, the problem of the same frequency or similar frequency band interference needs to be considered. For example, some known low-frequency points should be avoided, for example, the high frequency band needs to avoid the protection frequency range of the naval long river navigation system of China, namely 80-120 kHz, and the low frequency band needs to avoid the frequency points of 68.5kHz of the commercial hill platform and the japanese low-frequency time code jJY, namely 40kHz and 60kHz. In order to avoid interference with the second long river signal, 50kHz (since the center frequency of the second long river is 100 kHz) is avoided in view of the influence of the second harmonic.
In addition to the above frequency points, other interference frequency points may exist near the station, so that it is necessary to test the electromagnetic environment near the transmitting station in advance, count the frequency points with large low-frequency band field intensity, and try to avoid these frequency points in the low-frequency time code transmitting station frequency selection.
The reference steps of the electromagnetic environment test in this embodiment are as follows:
① Determining a test point: with the transmitting station as the center of a great circle and 200km as the radius of the great circle, test points are selected for each 5km of stepping quantity in eight directions of east, south, west, north, southeast, northeast, southwest and northwest.
② Atmospheric noise test: scanning each frequency point of the low frequency band, and recording the field intensity of each frequency point.
(3) Third screening, considering wave propagation factor
The low-frequency time code signal propagates in space in a continuous wave mode, and the space in which the antenna signal and the ground wave signal exist simultaneously. Specifically, in the range of 250-350 km, the ground wave is much stronger than the sky wave, and the ground wave is dominant; in the range of 350 km-2000 km, the space wave and the ground wave exist simultaneously to form an interference area; the low frequency signal is mainly sky wave beyond 2000 km.
In an interference area formed by the heaven and earth waves, heaven and earth wave signals are difficult to separate; meanwhile, due to the interference of the sky wave and the earth wave, the signal of a partial area is faded, and the signal to noise ratio of a receiving end is lower. Therefore, the range of the space-earth wave interference area and the characteristics of signal fading must be carefully studied, an electric wave propagation theoretical model is established, the distribution of the field intensity of each frequency point in the low-frequency band along with the distance is deduced according to the electric wave propagation theoretical model, and the frequency point with smaller field intensity fading is taken as a recommended frequency point.
In the embodiment of the invention, the estimation method of the low-frequency space-earth wave interference field intensity mainly comprises three main steps of ground wave field intensity estimation, space-earth wave phase difference estimation and space-earth wave superposition field intensity calculation. The field intensity distribution calculation method is given below:
the first step: the ground wave field intensity estimation, the propagation field intensity of the ground wave signal can be expressed as:
E(dB)＝109.54+20lgW-20lgd+10lgPΣ (1)
Wherein: d is the great circle distance between the receiving point and the transmitting point, and the unit is: km; w is the ground wave attenuation parameter; p Σ -transmit antenna radiation power in kw;
The path distances d, P Σ from equation (1) can be regarded as known quantities, and therefore the method of determining the ground wave attenuation parameter W is described below.
When the radiation source is a vertical monopole electric vibrator placed on the ground and the receiving point is also on the ground, the ground wave attenuation parameter W can be expressed as follows:
wherein, Known as phase constants or propagation factors, also known as wavenumbers; lambda is the wavelength (meter) of electromagnetic waves in the air; d is the great circle distance between the receiving point and the transmitting point, and the distance is expressed in meters.
The calculation is carried out in two cases:
1. When the distance between the receiving point and the transmitting point is smaller than 20km, the ground is regarded as a smooth and uniform plane, the formula for calculating F is called a flat ground model formula, and a convergence function form is adopted in the program. The introduced parameter-digital distance P is expressed as follows:
Where ε r =ε -j60deg.lambda.σ is the relative complex permittivity of the earth (ε is the earth relative permittivity and σ is the path conductivity).
F=r eF+jIm F is expressed in terms of a convergence series as:
The step number summation part in the simulation procedure takes the sum of the first 100 items.
2. When the distance between the receiving point and the transmitting point is more than 20km, the ground is regarded as a smooth spherical surface, and the atmosphere near the ground surface is taken as standard atmosphere.
At this time, F is solved by using the diffraction formula of Fock:
Wherein: (in the case of standard atmospheric conditions), is the equivalent earth radius; a= 6371.12km is the actual earth radius.
N is a large enough integer, and is determined according to the calculation precision of the series summation. The larger the distance, the faster the number of stages converges, and the smaller the N required, due to the convergence of the number of stages. Ensuring smooth continuity of the results of the short-range calculation, n=100 is usually taken.
T s is the differential equationIs the s-th complex root of (2).
And a second step of: space-earth wave phase difference estimation
Referring to FIG. 2, the radius of the earth is r, the height of the ionization layer is h, and for a certain point from the transmitting table d, half of the central angle of a sector area formed by the transmitting table and the earth center is(In radians); according to the cosine law,
s1＝r2+(r+h)2-2r(r+h)cosα (10)
Therefore, the propagation path of the one-hop sky wave is s=2s 1, and the propagation time difference between the one-hop sky wave and the ground surface is:
t0＝(s-d)/c (11)
let the period of the electromagnetic wave be T, the phase difference be
Wherein fix () represents a rounding.
And a third step of: field intensity estimation of space-earth wave synthesis interference field
The calculation of the sky wave field intensity is divided into two types of cases: a distance less than 1000km and a distance greater than 1000km.
1. D <1000 km:
The field intensity values of the sky wave are all calculated according to the field intensity value of the ground wave at 1000 km; the ground wave field strength at 1000 km is 512uv (h=68 km, p=60 KW). Thus:
E Total (S) (d)＝|E Ground wave (d)+512·sin(θ+90)| (13)
2. d is more than or equal to 1000 km:
The value of the field intensity of the sky wave is calculated according to the magnitude of the field intensity of the ground wave at a corresponding distance, namely, the value of the sky wave at 1000km is equal to the value of the ground wave at 1000 km; the value of the sky wave at 1200 km is equal to the value of the ground wave field strength at 1200 km. Thus:
E Total (S) (d)＝|E Ground wave (d)+E Ground wave sin(θ+90)| (14)
Where E Total (S) represents an estimated value of the superimposed field strength of the sky-ground wave, and E Ground wave represents an estimated value of the field strength of the ground wave.
After the calculation of the interference field intensity of the sky wave and the ground wave is finished, the frequency point set to be selected can be further screened according to the estimation result by combining the field intensity fading factors, the seasonal variation factors and the population distribution factors.
In particular in the embodiments of the present invention,
① The field intensity fading factor is calculated theoretically, and the situation that the antenna waves and the ground waves are mutually counteracted is relatively obvious in the interval of 700 km-1000 km away from the transmitting station, namely the field intensity is distributed in the interval along with the distance to possibly reach a local minimum value. In order to ensure the receiving effect of the receiving terminals in the area, only the frequency points with the distance range lower than the threshold value delta d are reserved by setting the lowest field intensity threshold value E min and the distance range threshold value delta d lower than the attenuation area corresponding to the threshold value E min.
② Factors of seasonal variation
Since the propagation of the sky wave refers to the wave formed by the low-frequency signal propagating through the way of ionosphere reflection, the height of the ionized layer has a direct influence on the propagation characteristic of the sky wave, and further influences the distribution result of the interference field intensity of the sky wave. Seasonal variations have a significant effect on the height of the ionised layer and therefore the distribution characteristics of the low frequency signal. Specifically, the height change of the ionization layer in winter and summer is most remarkable, so that the distribution of the field intensity of each frequency point in winter and summer along with the distance can be calculated according to the theoretical model, and the difference of the distribution in winter and summer is compared. And setting a correlation threshold value, and reserving frequency points with correlation larger than the threshold value.
③ Population coverage factor
From the perspective of the reception of low frequency time code signals, it is desirable that the decay region of the field intensity distribution avoid urban areas with relatively dense population as much as possible, so as to maximize the number of people receiving the most low frequency signals. According to field intensity theory calculation results, estimated values of design population of subsidence areas in different seasons are counted, a threshold value of the estimated value of the subsidence area population is set according to actual user group demands of the station, and frequency points of the estimated population of the subsidence area lower than the threshold value are screened and reserved.
(4) Fourth screening-frequency Generation factor
In order to improve the accuracy of the generated carrier signal and the reception accuracy in terms of generation of the low-frequency signal, it is considered to select a frequency point at which frequency synthesis is easier. Therefore, in the frequency point set screened in the first three steps, the common reference frequency generated by an atomic clock, such as integer frequency division of 10MHz, 5MHz, 10.23MHz, 2.048MHz and the like in low frequency band, is suggested to be used as a frequency point to be selected.
In summary, the present invention is set up for a low-frequency time code transmitting and broadcasting system, and provides a frequency selection method for a low-frequency time code time service signal, which analyzes the frequency selection problem from four aspects of generating, broadcasting, transmitting and receiving the low-frequency time code signal, comprehensively considers various factors including signal generation, effective radiation power of a transmitting antenna, near field interference, field intensity fading, influence of seasonal variation on low-frequency electric wave transmission, population coverage and frequency interference, and has the advantages of combining theory with actual measurement and comprehensively integrating.
The following are device embodiments of the present invention that may be used to perform method embodiments of the present invention. For details of the device embodiment that are not careless, please refer to the method embodiment of the present invention.
The embodiment of the invention provides a carrier frequency selection system of a low-frequency time code time service signal, which comprises the following steps:
The first screening module is used for carrying out frequency point first screening based on a preset antenna effective radiation power threshold value to obtain a first screening result;
the second screening module is used for carrying out frequency point second screening based on in-band interference factors to obtain a second screening result;
The third screening module is used for carrying out third screening on the frequency points based on the world wave interference characteristic factors to obtain a third screening result;
and the result acquisition module is used for screening according to the frequency generation factors based on the first screening result, the second screening result and the third screening result to obtain a final screening result, and completing the optimization of the carrier frequency of the low-frequency time code time service signal.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (6)
1. The carrier frequency selection method of the low-frequency time code time service signal is characterized by comprising the following steps of:
performing frequency point first screening based on a preset antenna effective radiation power threshold value to obtain a first screening result;
Performing frequency point secondary screening based on in-band interference factors to obtain a secondary screening result;
Performing third screening of frequency points based on the world wave interference characteristic factors to obtain a third screening result;
Based on the first screening result, the second screening result and the third screening result, screening according to frequency generation factors to obtain a final screening result, and completing carrier frequency selection of the low-frequency time code time service signals;
The step of performing third screening of the frequency points based on the world wave interference characteristic factors and obtaining a third screening result specifically comprises the following steps: calculating the field intensity distribution characteristics of the sky-earth waves of different frequency points according to the space-earth wave interference distribution estimation model to obtain an estimation result of the low-frequency space-earth wave interference field intensity; based on the estimation result of the low-frequency space-earth wave interference field intensity, combining field intensity fading factors, seasonal variation factors and population coverage factors to carry out low-frequency point screening, and obtaining a third screening result;
The step of calculating the field intensity distribution characteristics of the sky-earth waves of different frequency points according to the space-earth wave interference distribution estimation model to obtain the estimation result of the low-frequency space-earth wave interference field intensity specifically comprises the following steps:
The propagation field strength of the ground wave signal is expressed as E (dB) =109.54+20lgw—20lgd+10lgp Σ;
Wherein d-is the great circle distance between the receiving point and the transmitting point; w is the ground wave attenuation parameter; p Σ -transmit antenna radiation power;
the phase difference of the world wave is expressed as,
Wherein fix () represents rounding; t is the period of transmitting electromagnetic waves; the propagation time difference between the one-jump sky wave and the earth surface is t 0 = (s-d)/c; the propagation path of the one-hop sky wave is s=2s 1;
s 1＝r2+(r+h)2 -2r (r+h) cos α; wherein r is the earth radius; h is the ionization layer height;
d <1000 km: e Total (S) (d)＝|E Ground wave (d) +512·sin (θ+90°) |;
d is more than or equal to 1000 km: e Total (S) (d)＝|E Ground wave (d)+E Ground wave sin (θ+90°) |;
Where E Total (S) represents an estimated value of the superimposed field strength of the sky-ground wave, and E Ground wave represents an estimated value of the field strength of the ground wave.
2. The method for selecting carrier frequencies of low-frequency time-code time service signals according to claim 1, wherein the step of performing the first filtering of the frequency points based on the preset antenna effective radiation power threshold value to obtain the first filtering result specifically comprises:
Based on a preset antenna effective radiation power threshold value, calculating and obtaining a minimum value of frequency according to an empirical formula;
wherein the expression of the empirical formula is that,
Wherein P r is the radiation power; v t is the voltage of the effective top cap of the antenna; c is a capacitor; h e is the antenna effective height; f is the frequency of the broadcast.
3. The method for selecting carrier frequencies of low-frequency time-code time service signals according to claim 1, wherein the step of performing frequency point second screening based on in-band interference factors to obtain a second screening result specifically comprises:
Eliminating a preset known low-frequency station frequency point;
determining a test point, performing atmospheric noise test on a preset distance area of the test point, and eliminating frequency points with a test field intensity result larger than a preset threshold value.
4. The method for selecting carrier frequencies of low-frequency time-code time-service signals according to claim 1, wherein the step of screening low-frequency points based on the estimation result of the low-frequency space-earth wave interference field intensity and combining field intensity fading factors, seasonal variation factors and population coverage factors to obtain a third screening result specifically comprises:
Setting a minimum field intensity threshold E min and a distance range threshold Deltad lower than a decay region corresponding to E min when field intensity fading factors are combined, and screening frequency points with reserved distance ranges lower than Deltad;
when seasonal variation factors are combined, calculating to obtain the distribution of field intensity of each frequency point along with distance in winter and summer, and comparing the obtained differences of the distribution in winter and summer; setting a correlation threshold based on the difference, and screening frequency points with retained correlation larger than the correlation threshold;
And when the population coverage factors are combined, setting a population estimation value threshold of the subsidence area according to the preset user group demand of the station, and screening and reserving frequency points of which the population estimation value of the subsidence area is lower than the population estimation value threshold of the subsidence area.
5. The method for selecting carrier frequencies of low-frequency time-code time-service signals according to claim 1, wherein the step of selecting carrier frequencies of low-frequency time-code time-service signals by performing screening according to frequency generation factors to obtain final screening results based on the first screening result, the second screening result and the third screening result specifically comprises:
and based on the first screening result, the second screening result and the third screening result, adopting integer frequency division of the reference frequency generated by the atomic clock in the low frequency band as a screening result.
6. A low frequency time code time service signal carrier frequency selection system, comprising:
The first screening module is used for carrying out frequency point first screening based on a preset antenna effective radiation power threshold value to obtain a first screening result;
the second screening module is used for carrying out frequency point second screening based on in-band interference factors to obtain a second screening result;
The third screening module is used for carrying out third screening on the frequency points based on the world wave interference characteristic factors to obtain a third screening result;
the result acquisition module is used for carrying out screening according to the frequency generation factors based on the first screening result, the second screening result and the third screening result to obtain a final screening result, and completing carrier frequency selection of the low-frequency time code time service signals;
The step of performing third screening of the frequency points based on the world wave interference characteristic factors and obtaining a third screening result specifically comprises the following steps: calculating the field intensity distribution characteristics of the sky-earth waves of different frequency points according to the space-earth wave interference distribution estimation model to obtain an estimation result of the low-frequency space-earth wave interference field intensity; based on the estimation result of the low-frequency space-earth wave interference field intensity, combining field intensity fading factors, seasonal variation factors and population coverage factors to carry out low-frequency point screening, and obtaining a third screening result;
The step of calculating the field intensity distribution characteristics of the sky-earth waves of different frequency points according to the space-earth wave interference distribution estimation model to obtain the estimation result of the low-frequency space-earth wave interference field intensity specifically comprises the following steps:
The propagation field strength of the ground wave signal is expressed as E (dB) =109.54+20lgw—20lgd+10lgp Σ;
Wherein d-is the great circle distance between the receiving point and the transmitting point; w is the ground wave attenuation parameter; p Σ -transmit antenna radiation power;
the phase difference of the world wave is expressed as,
Wherein fix () represents rounding; t is the period of transmitting electromagnetic waves; the propagation time difference between the one-jump sky wave and the earth surface is t 0 = (s-d)/c; the propagation path of the one-hop sky wave is s=2s 1;
s 1＝r2+(r+h)2 -2r (r+h) cos α; wherein r is the earth radius; h is the ionization layer height;
d <1000 km: e Total (S) (d)＝|E Ground wave (d) +512·sin (θ+90°) |;
d is more than or equal to 1000 km: e Total (S) (d)＝|E Ground wave (d)+E Ground wave sin (θ+90°) |;
Where E Total (S) represents an estimated value of the superimposed field strength of the sky-ground wave, and E Ground wave represents an estimated value of the field strength of the ground wave.
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